The present invention relates to a process for the reduction of disadvantageous effects of engine stall torques on the braking behavior of a vehicle which is equipped with a brake unit having an anti-lock control system. A circuit arrangement for carrying out the process, also, is part of the invention.
In the event of low coefficients of friction, the engine stall torque, which is transmitted from the driving engine through the gearing to the driven wheels, can very rapidly lead to a brake torque which is excessive relative to the running stability of the driven wheels. This holds true, in particular, of high-power driving engines and when a low gear has been applied. As a result of this brake torque caused by the driving engine, the steerability is greatly reduced for a vehicle with front-wheel drive. In case of rear-wheel drive, there is even the risk of skidding. This phenomenon starts immediately upon the reduction of the driving power and may even be boosted by the operation of the brakes.
From published German patent application No. DE 4040256 Al, a circuit arrangement for a brake unit with anti-lock control system is known which triggers a test cycle if and when, during a control cycle, the two wheels of a driven axle signal instability beyond a preset lag of time. Due to the test cycle, brake pressure is controlledly supplied into the wheel brake of the slower wheel, and the reaction of the driven wheels to the controlled supply of pressure is evaluated. In this manner, the control system determines whether or not the matter involves effects of an engine stall torque. If this is the case, then, due to the controlled supply of pressure into the wheel brake of the slower wheel, the speed of the second wheel of this axle is increased through the differential and, as a result, the running stability and the lateral control are remarkably improved.
It is, moreover, prior art to prevent the transmission of the engine stall torque to the wheels by interfering with the driving line, that is to say by disengaging the clutch. This is complicated, especially because the correct moment for clutching again is difficult to determine.
Another possible solution to the problem involves reducing the brake torque which is transmitted to the driven wheels by increasing the engine speed with the aid of a stall torque control system.